1. Field of the Invention
The invention relates generally to the field of modulating a frequency or wavelength of electromagnetic waves, for example modulating laser frequencies when range-finding.
2. Background Information
When a laser is used to determine range or distance to an object, accuracy of the determined range depends on how accurately or precisely the light frequency or wavelength of the laser can be modulated. Accordingly, accurate and inexpensive methods for modulating laser frequencies are desirable.
In accordance with exemplary embodiments of the invention, a method and apparatus are provided for accurately and precisely modulating the wavelength and phase of a laser. An ADC (Analog to Digital Converter) is used to sample the output of a delay line discriminator (e.g., an inteferometer) translated to an intermediate frequency (IF) carrier. Quadrature components of the sampled output are generated and an arctangent function (e.g., atan2) is applied to convert the quadrature components to a phase measure that is proportional to the laser frequency. Correlator circuits are provided to extract average frequency, modulation peak deviation, and modulation phase error signals. Control-loop feedback using the extracted signals is used to adjust the average frequency, modulation deviation, and modulation phase to respective set points.